In general, a dual-input Fourier transform spectrometer (FTS) produces interferograms that have components of both even and odd symmetry. In addition to the desired interferogram contribution due to the source under study, which has even symmetry, each FTS output is often found to exhibit a component of odd symmetry that arises from the fact that the beam splitter is not ideal. Additionally, the beam splitter itself can be a source of emission that produces a modulated signal component at the output of the interferometer. An exploration of the effects, and correction, of nonideal beam-splitter characteristics in FTS interferograms is presented, including examples from the Herschel/SPIRE submillimeter wavelength imaging FTS.
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